Self-reactive T cells that escape negative selection in the thymus are potentially activated in the course of common infections. In order to avoid autoimmune diseases, the immune system developed several mechanisms to limit adaptive immune responses, including self-reactive ones, to the clearance of pathogens. Natural Killer (NK) T cells play a key role for regulation of adaptive immunity and are able to avert autoimmune disease in pre-clinical models. It is yet to be determined how NKT cells counter-regulate the pathogenesis of autoimmune diseases such as Type 1 Diabetes (T1D). Knowledge of mechanisms underlying NKT cell-mediated regulation could be instrumental to design new therapy to restore islet tolerance and preserve residual beta cell mass in T1D patients. Most of the difficulties so far encountered by studying those mechanisms could be due to activation and analysis of systemic NKT cells that may not be directly involved in prevention of the autoimmune process. We developed transgenic insCDId NOD mice that express the NKT cell restriction molecule, CD1d, within the pancreatic islets. In our transgenic model, CD1d expression induced local NKT cell activation and modulatory mechanisms that prevented autoimmune diabetes. We will take advantage of our unique transgenic model to analyze mechanisms by which NKT cells alter immunity within pancreatic tissues to perturb diabetogenesis. Specifically, we will address the following questions: Aim 1: Is a specific cytokine phenotype of NKT cells required for protection from autoimmune diabetes? We will analyze whether NKT cells, recruited to the site of autoimmunity by CD1d expression, carry a specific cytokine profile. Aim 2: Is the cytokine/chemokine microenvironment altered by activation of NKT cells within pancreatic islets? We will assess whether NKT cells locally alter the cytokine/chemokine profile towards a protective type that limits the inflammatory lymphocyte infiltration and favor recruitment of immune cells with regulatory function. Aim 3: Do NKT cells down regulate islet-reactive T cell responses by modulating dendritic cell (DC) function? We will address whether regulatory NKT cells modulate maturation state and tolerogenic function of DC. Aim 4: Do NKT cells favor recruitment of regulatory T cells such as Tr1 and CD4+CD25+ cells? We will test whether NKT cells, by acting on DC or the cytokine/chemokine environment, promote recruitment of T cell subsets able to suppress self-reactive T cells. [unreadable] [unreadable]